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Antioxidative Effect of Thymbra spicata
on Oxidative Stability of Palm and Corn
Oils
Sibel Yagcı a , Erdinc Yagcı b & Fahrettin Gogus c
a Karamanoğlu Mehmetbey University, Yunus Emre Campus ,
Karaman , Turkey
b ŞİMŞEK Biscuits and Food Industry and Trading Co. Ltd., Organized
Industrial Region , Karaman , Turkey
c
The University of Gaziantep, Engineering Faculty, Food Engineering Department , Gaziantep , Turkey
Accepted author version posted online: 05 Jul 2011.Published online: 17 Apr 2012.
To cite this article: Sibel Yagcı , Erdinc Yagcı & Fahrettin Gogus (2012) Antioxidative Effect
of Thymbra spicata on Oxidative Stability of Palm and Corn Oils, International Journal of Food Properties, 15:3, 656-664, DOI: 10.1080/10942912.2010.494761
To link to this article: http://dx.doi.org/10.1080/10942912.2010.494761
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International Journal of Food Properties, 15:656–664, 2012
Copyright © Taylor & Francis Group, LLC ISSN: 1094-2912 print / 1532-2386 online DOI: 10.1080/10942912.2010.494761
ANTIOXIDATIVE EFFECT OF THYMBRA SPICATA ON
OXIDATIVE STABILITY OF PALM AND CORN OILS
Sibel Yagcı
1, Erdinc Yagcı
2, and Fahrettin Gogus
31Karamano˘glu Mehmetbey University, Yunus Emre Campus, Karaman, Turkey 2¸S˙IM¸SEK Biscuits and Food Industry and Trading Co. Ltd., Organized Industrial
Region, Karaman, Turkey
3The University of Gaziantep, Engineering Faculty, Food Engineering Department,
Gaziantep, Turkey
In this study, modified rancimat method was used to determine the antioxidative effect of Thymbra spicata oil on the oxidative stability of corn and palm oils at various con-centrations of Thymbra spicata (1.39–5.49 mg mL−1) and temperatures (90, 100, and 120◦C). For a comparison, butylated hydroxyltoluene was used as a standard antioxidant.
Thymbra spicata oil was significantly effective on oxidation of both corn and palm oils at
concentrations used in this study. Specifically, the induction period of corn and palm oils was significantly elongated in the presence of Thymbra spicata oil. However, butylated hydrox-yltoluene was more effective against oxidation of oils than Thymbra spicata oil. Thymbra
spicata oil could be used as an easily accessible source of natural antioxidant for use in fats
and oils.
Keywords: Thymbra spicata, Rancimat method, Palm oil, Natural antioxidants, Lipid
oxidation.
INTRODUCTION
Lipid oxidation is one of the major factors that cause deterioration during the storage and processing of edible fats, oils, and fat-containing products. It modifies major qual-ity control parameters of fats ad oils, such as color, flavor, aroma, and nutritive value, affecting suitability for consumption.[1]The oils with higher contents of unsaturated fatty acids, especially polyunsaturated fatty acids, are more susceptible to oxidation due to their chemical structure. In order to overcome the stability problem of fats and oils, syn-thetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), are incorporated into fats and oils.[2]
Nowadays, consumers all over the world are becoming more conscious of the nutri-tional value and safety of their foods and food ingredients. Concurrently, there is a preference for natural foods and food ingredients that are believed to be safer, healthier, and less subject to hazards than their artificial counterparts.[3] However, the use of syn-thetic antioxidants in food products has been falling off due to their instability as well as due to a suspected action as promoters of carcinogenesis. Due to these safety concerns,
Received 12 February 2010; accepted 16 May 2010.
Address correspondence to Sibel Yagcı, Karamano˘glu Mehmetbey University, Engineering Faculty, Food Engineering Department, Yunus Emre Campus, Karaman 70100, Turkey. E-mail: syagci@kmu.edu.tr
656
EFFECT OF THYMBRA SPICATA ON STABILITY OF OILS 657
there is an increasing trend among food scientists to replace these synthetic antioxidants with natural ones, which, in general, are supposed to be safer.[4]It has been known for some time that the addition of certain aromatic herbs or spices to lipid containing materials will delay the oxidation process.[2]The antioxidant properties of many herbs and spices were reported to be effective in retarding the process of lipid oxidation in fats and oils.[1,2,4–6]
Thymbra spicata (Labiatae) grows wild in some eastern Mediterranean countries
and the dried leaves are used as a spice and as herbal tea. The major essential oils derived from Thymbra spicata have been reported to be carvacrol, thymol, E-3-caren-2-ol, andγ -terpinene, which have antioxidant and antibacterial activities.[7]It has been observed that antioxidant activity of 0.6 mg thyme extract (Thymus vulgaris L.) in 100 mL sunflower oil was as effective as that of 0.1 mg BHT when compared in reducing oxidative stability of sunflower seed oil.[8]Thyme extract inhibited the formation of hydroperoxides and gen-eration of pentanal and hexanal in sunflower oil during the incubation period at 60◦C.[6] The antioxidative activity and action mechanism of thymol and carvacrol were investigated during autoxidation of purified triacylglycerols of lard and sunflower oil containing various concentrations of thymol and carvacrol. The results obtained with inhibited lipid systems showed that thymol had the better antioxidant effectiveness and activity during triacylglyc-erols sunflower oil oxidation than carvacrol. It was interpreted that it is due to the greater steric hindrance of the phenolic group in thymol than in carvacrol.[9]In this study, effec-tiveness of natural antioxidant, Thymbra spicata, on the oxidation of two types of oils was demonstrated. The objectives of the present work were to (i) observe the effect of concen-tration of Thymbra spicata oil and temperature on the oxidative stability of both corn and palm oils and (ii) compare the antioxidant activity of Thymbra spicata oil with that of BHT.
MATERIALS AND METHODS Materials
Corn and palm oils that contained no added antioxidants were supplied from Marsa (Adana, Turkey). Thymbra spicata (Labiatae) was collected in Nizip, Gaziantep (South-Eastern Turkey). The leaves were separated from the branches and the air-dried leaves were stored in a polyethylene bag. Butylated hydroxytoluene (BHT) was purchased from Merck (Darmstad, Germany). Sodium sulphate, potassium bichromate, and sulphuric acid were purchased from Riedel De Haen (Seelze, Germany).
Extraction of Thymbra Spicata Oils
The separation of the essential oils from air dried Thymbra spicata was conducted by steam distillation in a Clavenger apparatus for 3 h. The oils were dried over anhydrous sodium sulphate, and stored in dark glass bottles until analysis. Various concentrations of
Thymbra spicata oil (1.39, 2.33, 4.29, and 5.49 mg mL−1) and BHT (0.014, 0.092, 1.400, and 2.400 mg mL−1) were added to corn and palm oils, respectively. BHT was used as a comparison synthetic antioxidant.
Measurement of Antioxidant Activity Using the Modified Rancimat Method
The apparatus used in the present study was based on the principles of both the active oxygen method and the Rancimat method. The Rancimat method is commonly
658 YAGCI, YAGCI, AND GOGUS
used to evaluate the antioxidative properties of various antioxidants and is based on the increase of electrical conductivity due to the formation of volatile dicarboxylic acids as a result of lipid oxidation.[10] In designed apparatus, the air was supplied by an air pump (Thomas Pump and Machinery Inc., Slidell, Los Angeles, CA, USA) and passed through a series of washing columns. The columns consisted of triple distilled water and 2% potassium bichromate in 1% sulphuric acid, respectively. A condenser was connected on the second column. Then the air was dried and filtered in a column containing glass wool and sodium sulphate. Washed, dried, and filtered air was compressed into a reac-tion vessel containing an oil sample. The reacreac-tion vessel was jacketed and heating oil was supplied from the heating bath (J.P. Selecta S.A, Barcelona, Spain) by the pump (J.P. Selecta S.A). The volatile compounds, which were formed in the reaction vessel, passed through a glass pipe into the absorption vessel and were trapped by triple distilled water in the absorption vessel. They changed the conductivity of the triple distilled water. The greater amount of volatile compounds formed was formic acid, which was probably pro-duced by the oxidative decomposition of aldehydes and ketones or organic peroxides. A second condenser was connected on the absorption vessel to prevent loss of volatile compounds. Measurements were controlled conductometrically with an electrode by using a conductivity-meter (Oakton Portable, Lab Depot Inc., Dawsonville, GA, USA).
The measurement of antioxidant was carried out for each oil sample by the following procedure. Approximately 50 mL of the oil sample was poured accurately into the reaction vessel and was then mixed with a preweighed amount of antioxidant. Then heating oil in the heating bath was pumped to the jacket of the vessel. The absorption vessel contain-ing an electrode of the conductivity-meter was filled with 400 mL of triple distilled water. When all the connections between the washing columns, reaction vessel, and absorption vessel were conducted, the reaction vessel was allowed to reach thermal equilibrium with the heating oil at selected temperatures (90, 100, and 120◦C) for a few minutes. The air flow rate was adjusted to 18 l/h. Conductivity change of triple distilled water was mea-sured at every fifteen minutes time intervals. A steep rise in conductivity showed that the reaction was completed. Measurement was conducted by Datalog Assist PC Software for Oakton Portable meters (Oakton Portable Version 1.0.0; Oakton Portable, Lab Depot Inc.). A control test for each oil type (with no additives) was included and subjected to the same experimental conditions. The induction time was determined by plotting the conductivities against time. The time (in min) taken to reach a specific conductivity value, correspond-ing to the flex point of the curve, was considered as the induction time. The longer the induction times, the greater were the antioxidant potencies of the compounds.
Analysis of Experimental Data
Statistical analysis of obtained data was made by using SPSS (version 11.0, SSPS Inc., Chicago, IL, USA) package program at 95% confidence interval. Bivariate corre-lations of Pearson’s two tailed tests was used to compare experimental data.
RESULTS AND DISCUSSION
Since the use of synthetic antioxidants has been questioned due to toxicity and possible carcinogenicity, there is considerable interest in developing plant-derived natu-ral antioxidants, especially from edible plants.[4] In this study, two types of oils (corn and palm), having different fatty acid composition, were investigated for their oxidative
EFFECT OF THYMBRA SPICATA ON STABILITY OF OILS 659
stability in the presence of Thymbra spicata oil and BHT. Different concentrations of
Thymbra spicata (1.39 to 5.49 mg mL−1) and BHT (0.014 to 2.400 mg mL−1) at various temperatures (90,100, and 120◦C) were studied for corn and palm oils as well as control oil samples with no added antioxidant. Corn oil has a high amount of unsaturated fatty acid, mainly linoleic acid, of up to about 62%. In addition to linoleic acid, corn oil has oleic acid in its composition, completing the unsaturated fatty acid composition of corn oil up to 82–88%. The remaining part is saturated fatty acids. Palm oil has about 50% saturated and 50% unsaturated fatty acid in its composition, respectively. Unsaturated fatty acid compo-sition of palm oil is mainly due to the oleic acid of up to about 50% and linoleic acid of up to about 11%. The remaining part of the palm oil composition is saturated fatty acids.[11]
Tables 1 and 2 tabulate induction times of corn and palm oils in the presence of various concentrations of Thymbra spicata and BHT at different temperatures. Induction periods of both corn and palm oils were significantly elongated in the presence of Thymbra
spicata and BHT as shown in these tables. When the induction times of corn and palm oils
at the same temperatures are compared, it can be easily seen that the induction time of palm oil without any antioxidant was greater than two-fold the induction time of corn oil. This was mainly due to the unsaturated fatty acid composition of palm oil containing approx-imately 25% less unsaturated fatty acids than the corn oil. Polyunsaturated components of fats are oxidized much more rapidly than monounsaturated and saturated components. In the time required to become rancid it is likely that only the polyunsaturated components undergo autoxidation; thus, it is the polyunsaturated components that are the focal points in
Table 1 Induction times of corn and palm oils with different concentrations of Thymbra spicata oil at various temperatures.
Induction times (min)
Oil type Temperature (◦C) Control 1.39 TSO 2.33 TSO 4.29 TSO 5.49 TSO
Corn oil 90 246 248 282 485 519 100 204 236 267 288 353 120 116 124 128 125 125 Palm oil 90 611 725 736 974 1126 100 457 518 586 656 805 120 254 279 287 291 296
TSO: Concentration of Thymbra spicata oil in mg ml−1.
Table 2 Induction times of corn and palm oils with different concentrations of BHT at various temperatures.
Induction times (min)
Oil type Temperature (◦C) Control 0.014 BHT 0.092 BHT 1.400 BHT 2.400 BHT
Corn oil 90 246 472 551 731 1, 141 100 204 428 513 596 950 120 116 138 152 168 253 Palm oil 90 611 984 1167 1539 2318 100 457 889 980 1191 1779 120 254 302 339 361 476 BHT: Concentration BHT in mg ml−1.
660 YAGCI, YAGCI, AND GOGUS
autoxidation of fats.[11]Generally, it is accepted that the higher the degree of unsaturation of an oil, the more susceptible it is to oxidative deterioration.[4]
Indeed, the induction time of both corn and palm oils increased significantly (p< 0.05) by addition of Thymbra spicata oil. Thymbra spicata oil contains a high amount of carvacrol (about 84%) and thymol (about 3%), which are isomers of each other.[7] These compounds show high antioxidant activity which is ascribed to hydrogen dona-tion and their ability to scavenge peroxyl radicals.[12]It was observed that[13]essential oils of thyme (45.3% thymol and 48.9% carvacrol) showed significant efficiency for prevent-ingα-tocopherol lost in olive oil heated at 180◦C. The authors revealed that essential oils of thyme exhibited properties as free radical-scavengers/antioxidants and could be used to control lipid oxidation during food processing. This was confirmed by results of other studies in the literature.[6,8,9]
As shown in Tables 1 and 2, BHT was more effective than Thymbra spicata oil in increasing oxidative resistance of both oil samples. There was up to a 2.11-fold increase in induction time of corn oil depending on the concentration and temperature. BHT prolonged induction time of corn oil about 2 to 4 times depending on concentration and temperature. Equally, the induction period of palm oil augmented up to about 1.8 and 3.8 in the presence of Thymbra spicata and BHT depending on concentration and temperature, respectively. The induction periods for Thymbra spicata were shorter than those for BHT, so the nat-ural antioxidant is less efficient than the synthetic additive (Figs. 1 and 2). In the present figures, the induction period for 1.40 mg mL−1of BHT concentration was given for com-parison of the effectiveness of two antioxidants. In this study, a 1.40 mg mL−1addition of BHT into both corn and palm oils caused about 1.5 times more increase in the induction times compared to the highest concentration of Thymbra spicata oil added. However, the use of Thymbra spicata oil as a natural antioxidant can be favorable. It is well known that maximum lawful levels for synthetic food additives are established from various toxico-logical parameters that need not be applicable to naturally-occurring compounds.[14]Thus,
Thymbra spicata oil could be used at higher levels than the synthetic counterparts, thereby
increasing their antioxidant effectiveness.
The addition of Thymbra spicata oil increased the induction periods of corn oil almost in all concentrations of added antioxidants and at studied temperatures except for 120◦C (Fig. 1c). At 90◦C, the addition of lower concentrations of Thymbra spicata oil (1.39 and 2.33 mg mL−1) showed little antioxidant efficiency compared to that of higher concentrations (4.29 and 5.49 mg mL−1). However, at 100◦C, the effectiveness of Thymbra
spicata oil increased linearly at increased concentrations as shown in Fig. 1b. Only at
120◦C, the induction period at the highest two concentrations of Thymbra spicata oil was very close to the lowest concentration of Thymbra spicata oil added. At the highest two concentrations of Thymbra spicata, oil induction times are the same (Table 1). It shows us that at 120◦C, an increase in the concentration of Thymbra spicata oil above a level does not cause any change in the induction period of corn oil. This may be attributed to the relatively low stabilizing effect of carvacrol and thymol, which have high volatilities at high temperatures.[9]The effect of BHT on the induction period of corn oil at 90, 100, and 120◦C was not the same as the Thymbra spicata (data not shown). An increase in the concentration of BHT increased the induction time of corn oil (Table 2). BHT does not have an optimum concentration, and the stability of fats to which it is added continues to increase with concentration.
Similar behaviors were observed for the palm oil; the increasing concentration of
Thymbra spicata extended the induction periods of palm oil at each studied temperature
EFFECT OF THYMBRA SPICATA ON STABILITY OF OILS 661 b Time (min) 0 100 200 300 400 500 600 700 Conductivity (µs) 0 20 40 60 80 100 120 * * * * * Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.40 mg ml–1 BHT a Time (min) 0 200 400 600 800 Conductivity (µs) 0 2 4 6 * * * * * Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.40 mg ml–1 BHT c Time (min) 0 50 100 150 200 250 Conductivity (µs) 0 50 100 150 Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.40 mg ml–1 BHT * * * *
Figure 1 Induction periods of corn oil with added Thymbra spicata oil. (a) 90◦C; (b) 100◦C; (c) 120◦C. TSO:
Thymbra spicata oil; BHT: butylated hydroxytoluene.∗Significantly different from the control at P< 0.05.
662 YAGCI, YAGCI, AND GOGUS b Time (min) 0 200 400 600 800 1000 1200 Con d u ctivity (µs) 0 10 20 30 40 50 60 * * * * * Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.40 mg ml–1 BHT c Time (min) 0 100 200 300 400 500 Co nd ucti v it y (µs) 0 20 40 60 80 Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.4 mg ml–1 BHT * * * * * Control 1.39 mg ml–1 TSO 2.33 mg ml–1 TSO 4.29 mg ml–1 TSO 5.49 mg ml–1 TSO 1.40 mg ml–1 BHT a Time (min) 0 200 400 600 800 1000 1200 1400 1600 Conduc tivi ty (µ s) 0 10 20 30 40 50 60 * * * * *
Figure 2 Induction periods of palm oil with added Thymbra spicata oil. (a) 90◦C; (b) 100◦C; (c) 120◦C. TSO:
Thymbra spicata oil; BHT: butylated hydroxytoluene.∗Significantly different from the control at P< 0.05.
EFFECT OF THYMBRA SPICATA ON STABILITY OF OILS 663
(Fig. 2). At 120◦C, the effect of increasing concentration of Thymbra spicata oil was not so high (Fig. 2c). There was an increase in the induction period of up to about 16% with the highest concentration used at 120◦C. As the temperature decreased, induction periods of palm oil increased. As well, the effect of increasing concentration of Thymbra spicata oil was not high compared to BHT (data not shown), but its effect could not be neglected. From these results, it can be said that as the temperature decreased, the effectiveness of
Thymbra spicata increased in both corn and palm oils. That might be due to volatility of
the Thymbra spicata oil at high temperatures. An increase in temperature was probably increasing the volatility of the Thymbra spicata oil.
In this study, a change in induction periods of both corn and palm oils, with no antioxidant added, showed that the increase in the temperature caused a decrease in the induction periods (Figs. 1 and 2). An increase in temperature by 10◦C (90 to 100◦C) caused about a 17 and 25% decrease in induction times, while a 20◦C (100 to 120◦C) increase in temperature caused about a 43 and 45% decrease in induction times of the corn and palm oils, respectively (Table 1). From accelerated tests on many samples of commercial animal and fat shortenings, it has been established that the average rate of oxidation at 110◦C is about 2.5 times that at 97.8◦C; this corresponds to a doubling interval of 9◦C.[11]
Results obtained from the rancimat testing of corn and palm oils showed that
Thymbra spicata oil was significantly effective on controlling oxidation in oils. In an
earlier study, it was stated that the corn oil supplemented with 0.2% sesamol heated at 180◦C for 3 h was significantly more stable than the control sample.[15] Similarly, the addition of 0.02% extract from the root of Rumex japonicus Houtt to corn oil increased its oxidative stability about 1.8-fold determined at 60◦C.[16] The effectiveness of Thymbra
spicata on oxidation of the palm oil was also significant. Nor et al.[17] observed that the extracts of Pandanus amaryllifolius leaf (optimum concentration 0.2%) significantly retarded palm olein oxidation and deterioration, comparably to 0.02% BHT as similar to our study.
CONCLUSION
From the present study, it can be concluded that Thymbra spicata extract with high antioxidant activity can stabilize corn and palm oils at various concentrations added. Adding Thymbra spicata oil into both corn and palm oils prolonged induction times of oils up to 2.1- and 1.8-fold compared to control oil samples, respectively. The results of this study indicated that palm oil was more stable than corn oil, and BHT is more effective against oxidation of oil than Thymbra spicata. In conclusion, Thymbra spicata oil could be used as an easily accessible source of natural antioxidant for use in fats and oils.
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